Before the discovery of electromagnetic radiation known as x-rays, techniques and procedures in the field of dentistry were based on purely empirical knowledge. On Nov. 8, 1895, William Conrad Roentgen announced the discovery of this new kind of radiation. Within fourteen days, Otto Walkhoff, a German dentist, took the first dental radiograph of his own mouth. Dr. William James had completed several dental radiographs five months later. In 1913, Coolidge improved the manufacturing techniques of the x-ray tube, which allowed for better control of the quality and quantity of radiographs. The panoramic x-ray device was invented in 1950. During many decades, the use of film-based radiography dominated these trends in dentistry.
Dental digital radiography is a form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce a 2D still image of similar contrast to conventional film-based radiography. Some types of digital dental radiography sensors are small and thin enough that they can be placed intraorally or inside the mouth. Others are larger in size and are used extraorally or outside the mouth in order to obtain a dental image. The first intraoral X-rays imaging sensor available on the market was introduced following the principles described in U.S. Pat. No. 4,593,400 and U.S. Pat. No. 5,382,798 of Mouyen, 1986 and 1995 respectively based on a scintillating material and a charged coupled device (CCD) technology. Other inventions in the field used similar CCD sensors such as in U.S. Pat. No. 5,434,418 of Schick, 1995, U.S. Pat. No. 5,510,623 of Savag et al. and U.S. Pat. No. 5,693,948 of Sayed et al., 1996 and 1997 respectively and U.S. Pat. No. 5,519,751 of Yamamoto et al., 1996. Another particular type of digital system which uses a memory phosphor plate in place of the film is introduced in U.S. Pat. No. 4,965,455 of Schneider et al., 1990. The digitized images are stored, scanned and then displayed on the computer screen. This method is halfway between old film-based technology and current direct digital imaging technology. It is similar to the film process because it involves the same image support handling but differs because the chemical development process is replaced by the scanning process. The complementary metal-oxide-semiconductor (CMOS) active pixel sensor technology was proposed to dentistry in U.S. Pat. No. 5,912,942 of Schick et al., 1999 which provided advantages such as competitive wafer processing pricing, and on chip timing, control and processing electronics when compared to the CCD technology. Other inventions in the field utilizing similar CMOS technology are included in U.S. Pat. No. 6,404,854 of Carrol et al., 2002, U.S. Pat. No. 7,211,817 of Moody, 2007, U.S. Pat. No. 7,615,754 of Liu et al., 2009, and in U.S. Pat. No. 7,608,834 Boucly et al., 2009 which introduced some improvements through the description of the biCMOS technology combining bipolar transistors and CMOS devices. Due to the rigidity of these intraoral sensors which translated in patient's discomfort while placed inside the mouth, a flexible sensor using thin film transistors technology was devised in U.S. Pat. No. 7,563,026 of Mandelkern et al., 2009 trying to reproduce the comfort of conventional film.
On the other hand, the use of flat panel detectors in dentistry has been focused in the cephalometric, orthopantomographic, scannographic, linear tomographic, tomosynthetic and tomographic fields for 2D and 3D extraoral radiography. These principles are illustrated in the U.S. Pat. No. 5,834,782 of Schick et al., 1998, U.S. Pat. No. 7,016,461, U.S. Pat. No. 7,197,109 and U.S. Pat. No. 7,319,736 of Rotondo et al, 2006, 2007 and 2008 respectively, U.S. Pat. No. 7,136,452 and U.S. Pat. No. 7,336,763 of Spartiotis et al., 2006 and 2008 respectively and U.S. Pat. No. 7,322,746 of Beckhaus et al., 2008. The problem with all these existing dental digital intraoral and extraoral radiography technologies is that their final outcome is either 2D or a 3D still image.
Fluoroscopy is a dynamic x-ray, or x-ray movie showing images of video frame rates. It differs from dental digital radiography in that dental digital radiography is static x-ray, or an x-ray picture. An analogy is that of a movie compared to a snapshot. The beginning of fluoroscopy can be traced back to 8 Nov. 1895 when Wilhelm Roentgen noticed a barium platinocyanide screen fluorescing as a result of being exposed to what he would later call x-rays. The fluoroscopic image obtained in this way was rather faint. Thomas Edison quickly discovered that calcium tungstate screens produced brighter images and is credited with designing and producing the first commercially available fluoroscope. The first fluoroscope for dental use was described by William Herbert Rollins in 1896. Due to the limited light produced from the fluorescent screens, early radiologists were required to sit in a darkened room in which the procedure was to be performed, getting their eyes accustomed to the dark and thereby increasing their sensitivity to the light. The placement of the radiologist behind the screen resulted in significant radiation doses to the radiologist. Red adaptation goggles were developed by Wilhelm Trendelenburg in 1916 to address the problem of dark adaptation of the eyes, The resulting red light from the goggles' filtration correctly sensitized the physician's eyes prior to the procedure while still allowing him to receive enough light to function normally. The invention of X-ray image intensifiers in the 1950s allowed the image on the screen to be visible under normal lighting conditions, as well as providing the option of recording the images with a conventional camera. Subsequent improvements included the coupling of, at first, video cameras and, later, video CCD cameras to permit recording of moving images and electronic storage of still images. Medical fluoroscopes also known as C-arms or mini C-arms are too large to fit in a dental operatory. The main reason is the size of one of their main components: >6 inches diameter image intensifiers. However, recent breakthroughs in imaging and night vision technologies made possible the miniaturization of the medical fluoroscope for dental use as disclosed in the U.S. Pat. No. 6,543,936 of Feldman, 2003 by using small image intensifiers. Night vision image intensifiers (18-40 mm diameter)—like those used for military purposes—can convert fluoroscopy's low-radiation beam—after going through the patient's dental area—on a vivid video image. This image can be captured by a video digital camera chip and then displayed in real-time video on a monitor. Consequently, this breakthrough has allowed the fluoroscopy technology to fit in a dental operatory. Another attempt to reduce the medical fluoroscope size is seen in foreign Patents No. WO/2004/110277, WO/2005/072615 and WO/2005/110234 of Kim, 2004, 2005 and 2005 respectively. Despite these efforts, the image receptor configuration using the image intensifier and camera is still too bulky to be used inside the mouth and not ergonomic for the dentist to be placed extraorally while performing treatments on patients. Also, the proposed configurations in previous inventions only disclose the use of fluoroscopy in a 2D approach using image intensifiers.
However, more modern medical technology improvements in flat panel detectors have allowed for increased sensitivity to X-rays, and therefore the potential to reduce patient radiation dose. The introduction of flat-panel detectors in for 2D fluoroscopy in medicine as illustrated in the U.S. Pat. No. 5,262,649 of Antonuk et al., 1993, U.S. Pat. No. 5,610,404 and U.S. Pat. No. 5,648,654 of Possin, 1997 respectively, U.S. Pat. No. 5,773,832 of Sayed et al., 1998, U.S. Pat. No. 5,949,848 of Giblom, 1999, U.S. Pat. No. 5,962,856 of Zhao et al., 1999, U.S. Pat. No. 6,566,809 of Fuchs et al., 2003, U.S. Pat. No. 6,717,174 of Karellas, 2004, U.S. Pat. No. 7,231,014 of Levy, 2007, U.S. Pat. No. 7,323,692 of Rowlands et al., 2008, U.S. Pat. No. 7,426,258 of Zweig, 2008, U.S. Pat. No. 7,629,587 of Yagi, 2009 allows for the replacement of the image intensifier in the medical fluoroscope design. Temporal resolution is also improved over image intensifiers, reducing motion blurring. Contrast ratio is also improved over image intensifiers: flat-panel detectors are linear over very wide latitude, whereas image intensifiers have a maximum contrast ratio. Medical fluoroscopy 3D approaches have been described in the U.S. Pat. No. 5,049,987 of Hoppenstein, 1991 utilizing a plurality of image capture devices arranged in a predetermined pattern, in the U.S. Pat. No. 5,841,830 of Barni et al., 1998 where a motor is used to rotate the emitter and detector around the patient body and in the U.S. Pat. No. 7,596,205 of Zhang et al., 2009 in which the X-ray radiography unit irradiates a subject with X-rays from first X-ray tube to obtain an X-ray radiographic image. The X-ray CT unit irradiates the subject with X-rays from the second X-ray tube and acquires projection data from a beam of the X-rays that has passed through the subject, to reconstruct an image using the acquired projection data, and to obtain a tomographic image.
As has been shown, all these inventions are designed to be used on a medical setting. They are too large to be used for dental purposes. Consequently, none of these dental and medical technologies offer a flat panel, an emitter in a C-arm/U-arm and an O-arm configuration suitable for 2D and 3D dental fluoroscopy.